In the processing of grains, such as the wet milling of corn, waste water or effluent containing organic biomass is produced. The waste water will have a certain biological oxygen demand (BOD), which may vary depending on the type of processing occurring at the facility. If the BOD is high enough, it must be reduced to acceptable levels before the waste water is reintroduced to the environment. Typically, the waste water will be introduced into an anaerobic digester to help break down the organic material in the waste water to reduce its BOD. During the anaerobic digestion process, microorganisms such as bacteria in the waste water break up the organic material and gases, such as carbon dioxide, methane, and nitrogen are released. It is desirable to remove these gases from the waste water for a number of reasons. For example, methane produced can be captured and used in other industrial processes as an energy source.
Because the treatment process is continuous, microorganisms needed for the digestion process frequently need to be replenished. However, the gases created during anaerobic digestion can adversely affect the water treatment process by hindering the recapture of these microorganisms. In particular, the gases released during anaerobic digestion can tend to cling to the microorganisms, causing them to float. This is problematic, because in order to isolate and recapture the microorganisms, they must be allowed to settle in a settling tank to prevent them from being sent to further treatment and eventually being disposed of when the fully treated water is released. A polymer, such as a cationic polyacrylamide polymer, may be added to the waste water prior to entering the settlement tank to help flocculate the remaining biomass, which promotes sedimentation of the solids. However, if insufficient microorganisms are recovered from the digestion process, the capacity of the anaerobic digester will be reduced, thereby reducing upstream production capacity.
In order to remove gas from the waste water after the anaerobic digestion process, the waste water is introduced into a degassing tank. Prior known methods for degassing waste water, such as by an agitator, may not sufficiently remove gas from the waste water, particularly when the flow rate of waste water or the BOD load is relatively high. Further, space limitations can rule out other known methods of degassing. Thus, improvement in the degassing of waste water is desirable.